The government website launched this week to sell health insurance was overwhelmed by up to five times as many users as it was designed to handle, President Obama's top technology adviser said Saturday in an exclusive interview with USA TODAY.

U.S. Chief Technology Officer Todd Park said the government expected HealthCare.gov to draw 50,000 to 60,000 simultaneous users, but instead it has drawn as many as 250,000 at a time since it launched Oct. 1.

Park's comments are the administration's most detailed explanation for the glitches that have frustrated millions of consumers who have tried to enter the site or complete applications for health insurance under the Affordable Care Act.

"These bugs were functions of volume,'' Park said. "Take away the volume and it works.''

The administration built the site's capacity based partly on the all-time high of 30,000 simultaneous users for Medicare.gov, an existing site where senior citizens can buy or renew prescription-drug plans under Medicare Part D, Park said. Its theoretical maximum capacity hasn't been disclosed.

More than 8.1 million consumers visited the site from Tuesday through Friday, according to the White House. The administration hopes that as many as 7 million consumers eventually will sign up for health insurance through the government marketplace.

HealthCare.gov's enrollment functions are shut down at off-peak hours this weekend so technicians can make repairs to the site.

``We're obviously not satisfied with the performance,'' Park said. ``We're working 24-7.''

The site will be running better by early next week, he said, though he declined to make specific guarantees. The administration isn't yet prepared to say how many simultaneous users the upgraded site will be able to handle, he added.

The administration's explanation didn't impress a Bush administration official who helped launch Part D in 2006.

"Whoever thought it would draw 60,000 people wasn't reading the administration's press releases,'' said David Brailer, former national coordinator of health care information technology. "The Medicare Part D site was supposed to have 20,000 simultaneous users and was (built for) 150,000, and that was back when computing was done on an abacus. It isn't that hard.''

The volume since Tuesday overwhelmed a specific component of software on the HealthCare.gov site that lets people create accounts, enabling them to shop for insurance plans available in their state, Park said.

The part of the site that explains generally how the new law will work, and gives broad information about the kinds of plans available, has worked throughout the troubled launch, he said.

The Affordable Care Act called for the Department of Health and Human Services to build an online exchange, or Internet store, to let uninsured consumers compare and buy plans offered by private insurance companies. The government will subsidize coverage for many working-class and middle-class families, while poorer citizens may be covered by the law's expansion of the existing Medicaid program for low-income families.

The exchange misfired almost immediately upon its launch.

This photo provided by HHS shows the main landing web page for HealthCare.gov.(Photo: AP)

Engineers quickly deployed software that referred visitors to an online waiting room, hoping that controlling the number of people trying to create accounts would ease pressure on the software, Park said. But serious performance issues have plagued the site all week, he said.

Park disputed a Reuters report that quoted non-government technology experts who theorized that the site's architecture inadvertently made it mimic a common method by which hackers attack websites to shut them down, forcing the software to misfire.

"That is not the driver of the bottleneck,'' he said.

The site is managed by the Center for Medicare and Medicaid Services, Park said. It is hosted at a secure, privately owned cloud computing facility in Virginia. Outside experts this week had questioned whether the site was being run on cloud-based technology, whose flexibility usually lets website owners adjust quickly to spikes in traffic.

But the problem proved to be more complex than just adding more computer servers to manage the extra demand, he said.

A team working on the site is taking two other steps to fix the problem, Park said.

It is upgrading software that lets people create accounts to apply for insurance. One symptom of this has been malfunctioning pull-down menus that have worked only intermittently all week. And HealthCare.gov is moving one part of the site that processes applications from so-called virtual machine technology, which uses software to let a website securely share computer servers with other sites, to using servers dedicated exclusively to that process, he said.

That change will add extra computing power, complementing the software upgrade to make the registration process work more smoothly, he said.